A conventional method for displaying a picture includes a method for decoding the whole compressed picture, storing the decoded picture in a large memory, copying data to be displayed to a frame memory, and outputting the data on a display screen, and a method for reading a file to be displayed by using a special compression algorithm, and displaying necessary data with the help from hardware.
The method for decoding the whole picture, storing the decoded picture in the large memory, copying the data in the corresponding position to a frame buffer by scrolling the display screen, and outputting the data to the display screen decodes compressed picture streams at a time and stores the decoded picture in the memory. Therefore, if the picture has high resolution, a large capacity of memory is needed. Accordingly, this method is not suitable for a portable terminal apparatus having small system resources.
For example, 4 Mbyte of memory is used to decompress and store a picture having the resolution of 1024 pixels in width and 2048 pixels in length in a terminal using display screen that supports 16 bit colors. In addition, when the compressed picture is decompressed and stored in the memory, an initial delay time increases.
The method for decoding and displaying specific data decodes and displays the data in the corresponding position, by scanning the whole compressed streams. Thus, this method can be used in a special compression algorithm.
For example, when the picture is compressed in block units like JPEG, the block data compressed streams in a decoding position are searched by scanning the whole file, and restored and displayed. It is dependent upon a method for compressing a picture. In the case that the method for compressing the picture maintains dependency of data, some compressed streams may not be restored. Moreover, the whole file must be scanned to compose one display screen, which requires a high speed hardware apparatus.
On the other hand, when the resolution of the picture is different from the resolution of the terminal for outputting the picture, the resolution of the picture must be converted in accordance with the resolution of the terminal. That is, when picture data are outputted to a terminal having a low resolution display means such as a mobile communication terminal, the picture is outputted with the resolution supportable by the terminal.
However, while the picture data are converted to have the low resolution, they are seriously damaged and lost, which reduces quality of picture.